I have twin bbc and my one alternator when i apply the 12v power supply to the back on it it will start squealing and getting hot I tried new grounds two new alternators brand new battery’s. I’m lost can anyone help me ?

are you applying 12v to where the purple wire goes?

theres also a large fuse down by the batt connection on the starter

No. At least I don’t think so. That’s just the key hot wire correct ?

This photo is helpful. You can also click on it a few times to make it bigger. :thumbs